Olefin polymerization catalysts are of great use in industry. Hence there is great interest in finding new catalyst compounds, particularly compounds that can be easily supported and or modified by altering the ligands. There also exists the need to reduce catalyst costs by developing catalyst systems that are efficient utilizing simple alkyl aluminums rather than alumoxanes which are traditionally more expensive.
Silica supported chromium tris(amide)/alumoxane olefin polymerization catalysts are found in U.S. Pat. No. 6,040,399 where calcining at greater than 500° C. is disclosed to reduce polyethylene molecular weight (column 4, line 24). Further the U.S. Pat. No. 6,040,399 examples use Cr(III) tris(trimethylsilyamide) which may or may not react with the support and as noted they found only formation of oligomers if using silica calcined above 500 C. Further in U.S. Pat. No. 6,040,399, comparative example 4, describes a catalyst system with a supported Cr(III) tri(trimethylsilyamide) catalyst activated with triisobutylaluminum yielding an extremely low activity polymerization catalyst.
U.S. Pat. No. 6,011,127 discloses a process for making polyethylene comprising polymerizing ethylene in the presence of a supported catalyst comprising a chromium compound such as a chromium amide, an alumoxane, and an organometallic alkoxide.
U.S. Pat. No. 5,723,399 discloses an ethylenic polymerization catalyst comprising a chromium compound, a carrier, alumoxane, and a transition metal compound having a conjugated π (Pi) electron as a ligand, where in the chromium compound is not calcined.
Additional references that are of interest include: JP-11092522 A2 (199-04-06), JP-11228620 (1999 08-24), JP-10338707 (1998-12-22), Enders, M.; Fernandez, P.; Ludwig, G.; Pritzkow, H. Organometallics 2001, 20, 5005-5007, Theopold, K. H.; Eur. J. Inorg. Chem. 1998, 15., Karapinka., G. L. U.S. Pat. No. 3,709,853; 1973, Hogan, J. P.; and Banks, R. L. U.S. Pat. No. 2,825,721, 1958.